Papers on halocarbon concentrations in the atmosphere

Posted by Ari Jokimäki on May 8, 2010

This is a list of papers on the atmospheric concentration of halocarbons. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

Tropospheric halocompounds and nitrous oxide monitored at a remote site in the Mediterranean – Artuso et al. (2010)“Analysis of time series and trends of nitrous oxide (N2O) and halocompounds weekly monitored at the Mediterranean island of Lampedusa are discussed. … CFC-11 and CFC-12 time series displayed a decline consistent with their phase-out. Chlorofluorocarbons (CFCs) replacing compounds and SF6 exhibited an increasing temporal behaviour. The most rapid growth rate was recorded for HFC-134a with a value of 9.6 % yr−1. The industrial solvents CCl4 and CH3CCl3, banned by the Montreal Protocol, showed opposite trends. While CH3CCl3 reported an expected decay of -1.8 ppt yr−1, an increasing rate of 5.7 ppt yr−1 was recorded for CCl4 and it is probably related to its relatively long lifetime and persisting emissions. Chlorinated halomethanes showed seasonality with a maximum in early April and a minimum at the end of September. Halon-1301 and Halon-1211 displayed a decreasing trend consistent with industry emission estimates. An interspecies correlation analysis gave positive high correlations between HCFC-22 and HFC-134a (+0.84) highlighting the common extensive employment as refrigerants. Sharing sources inferred the high coupling between CH3Cl and CH3Br (+0.73) and between CHCl3 and CH2Cl2 (+0.77). A singular strong relationship (+0.55) between HFC-134a and CH3I suggested the influence of an unknown anthropogenic source of CH3I. Constraining of source and sink distribution was carried out by transport studies. Results were compared with the European Environment Agency (EEA) emission database. In contrast with the emission database results, our back trajectory analysis highlighted the release of large amounts of HFC-134a and SF6 from Eastern Europe. Observations also showed that African SF6 emissions may be considerable. Leakages from SF6 insulated electrical equipments located in the industrialized Northern African areas justify our observations.”

Accelerating growth of HFC-227ea (1,1,1,2,3,3,3-heptafluoropropane) in the atmosphere – Laube et al. (2010)“We report the first measurements of 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea), a substitute for ozone depleting compounds, in air samples originating from remote regions of the atmosphere and present evidence for its accelerating growth. Observed mixing ratios ranged from below 0.01 ppt in deep firn air to 0.59 ppt in the current northern mid-latitudinal upper troposphere. Firn air samples collected in Greenland were used to reconstruct a history of atmospheric abundance. Year-on-year increases were deduced, with acceleration in the growth rate from 0.029 ppt per year in 2000 to 0.056 ppt per year in 2007. Upper tropospheric air samples provide evidence for a continuing growth until late 2009. Furthermore we calculated a stratospheric lifetime of 370 years from measurements of air samples collected on board high altitude aircraft and balloons. Emission estimates were determined from the reconstructed atmospheric trend and suggest that current “bottom-up” estimates of global emissions for 2005 are too high by a factor of three.” [Full text]

Global carbon tetrachloride distributions obtained from the Atmospheric Chemistry Experiment (ACE) – Allen et al. (2009)“The first study of the global atmospheric distribution of carbon tetrachloride (CCl4), as a function of altitude and latitude, was performed using solar occultation measurements obtained by the Atmospheric Chemistry Experiment (ACE) mission using Fourier transform spectroscopy. A total of 8703 profile measurements were taken in the upper troposphere and lower stratosphere between February 2004 and August 2007. The zonal distribution of carbon tetrachloride displays a slight hemispheric asymmetry and decreasing concentration with increasing altitude at all latitudes. Maximum carbon tetrachloride concentrations are situated below 10 km in altitude with VMR (Volume Mixing Ratio) values of 100–130 ppt (parts per trillion). The highest concentrations are located about the Equator and at mid-latitudes, particularly for latitudes in heavily industrialised regions (20–45° N), with values declining towards the poles. Global distributions obtained from ACE were compared with predictions from three chemistry transport models showing good agreement in terms of the vertical gradient despite an overall offset. The ACE dataset gives unique global and temporal coverage of carbon tetrachloride and its transport through the atmosphere. An estimated lifetime for carbon tetrachloride of 34±5 years was determined through correlation with CFC-11.” [Full text]

A 2000 year atmospheric history of methyl chloride from a South Pole ice core: Evidence for climate-controlled variability – Williams et al. (2007)” This study presents CH3Cl measurements in air extracted from a 300 m ice core from South Pole, Antarctica, covering the time period from 160 BC to 1860 AD. The data exhibit an increasing trend of 3 ppt (parts per trillion) over 100 years and higher frequency variations that appear to be climate-related. CH3Cl levels were elevated from 900–1300 AD by about 50 ppt relative to the previous 1000 years, coincident with the warm Medieval Climate Anomaly (MCA). CH3Cl levels decreased to a minimum during the Little Ice Age cooling (1650–1800 AD), before rising again to the modern atmospheric level of 550 ppt. These variations most likely reflect changes in tropical and subtropical conditions, and raise the possibility that a warmer future climate may result in higher tropospheric CH3Cl levels.” [Full text]

Ambient halocarbon mixing ratios in 45 Chinese cities – Barletta et al. (2006)“During this study 158 whole air samples were collected in 45 Chinese cities in January and February 2001. The spatial distribution of different classes of halocarbons in the Chinese urban atmosphere, including chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), Halon-1211, and other chlorinated compounds is presented and discussed. Most of these compounds were enhanced compared to background levels. However, the mean enhancement of CFCs was relatively small, with CFC-12 and CFC-11 increases of 6% (range 1–31%) and 10% (range 2–89%), respectively, with respect to the global background. On the contrary, strongly enhanced levels of CFC replacement compounds and halogenated compounds used as solvents were measured. The average Halon-1211 concentration exceeded the background of 4.3 pptv by 75% and was higher than 10 pptv in several cities. Methyl chloride mixing ratios were also strongly elevated (78% higher than background levels), which is likely related to the widespread use of coal and biofuel in China.” [Full text]

Trends of halon gases in polar firn air: implications for their emission distributions – Reeves et al. (2005)“Four halons (H-1301, H-1211, H-2402 and H-1202) have been measured in air samples collected from polar firn from Dome Concordia (Dome C), Antarctica, from Devon Island, Canada and the North Greenland Ice Core Project (NGRIP) site, Greenland. H-2402 and H-1202 are reported for the first time in firn air. The depth profiles show the concentrations of all four halons to be close to zero (i.e. below the detection limit of 0.001 ppt) at the base of the firn thus demonstrating their entirely anthropogenic origin. This is the first evidence of this for H-2402 and H-1202.” [Full text]

Analyses of firn gas samples from Dronning Maud Land, Antarctica: Study of nonmethane hydrocarbons and methyl chloride – Kaspers et al. (2004)“Firn air was sampled on the Antarctic plateau in Dronning Maud Land (DML), during the Norwegian Antarctic Research Expedition (NARE) 2000/2001. In this paper, we describe the analyses for methyl chloride and nonmethane hydrocarbons (NMHCs) in these firn air samples. For the first time, the NMHCs ethane, propane, and acetylene have been measured in Antarctic firn air, and concentration profiles for these gases have been derived. A one-dimensional numerical firn air diffusion model was used to interpret the measured profiles and to derive atmospheric concentrations as a function of time. The atmospheric trends we derived for the NMHC and methyl chloride at DML cover the period from 1975 to 2000. Methyl chloride shows a decreasing trend of 1.2 ± 0.6 ppt per year (annual mean concentration 548 ± 32 ppt). For ethane we found an increasing trend of 1.6 ± 0.6 ppt per year (annual mean concentration 241 ± 12 ppt). The concentrations of propane and acetylene appear to be constant over the period 1975–2000, with annual mean concentrations of 30 ± 4 ppt for propane and 24 ± 2 ppt for acetylene.” [Full text]

Atmospheric variability of methyl chloride during the last 300 years from an Antarctic ice core and firn air – Aydin et al. (2004)“Measurements of methyl chloride (CH3Cl) in Antarctic polar ice and firn air are used to describe the variability of atmospheric CH3Cl during the past 300 years. Firn air results from South Pole and Siple Dome suggest that the atmospheric abundance of CH3Cl increased by about 10% in the 50 years prior to 1990. Ice core measurements from Siple Dome provide evidence for a cyclic natural variability on the order of 10%, with a period of about 110 years in phase with the 20th century rise inferred from firn air. Thus, the CH3Cl increase measured in firn air may largely be a result of natural processes, which may continue to affect the atmospheric CH3Cl burden during the 21st century.” [Full text]

Halocarbons and other Atmospheric Trace Species – Thompson et al. (2004)“Sustained measurement programs within HATS are based upon in situ and flask measurements of the atmosphere from the five CMDL baseline observatories and ten cooperative stations… … Most major CFCs and CCl4 are decreasing at a slow rate, while CH3CCl3 has decreased in the troposphere to mixing ratio levels below 25 parts per trillion (ppt, 10-12).” [Full text]

Methyl bromide in preindustrial air: Measurements from an Antarctic ice core – Saltzman et al. (2004)“This paper presents the first ice core measurements of methyl bromide (CH3Br). Samples from a shallow Antarctic ice core (Siple Dome, West Antarctica), ranging in mean gas dates from 1671 to 1942, had a mean CH3Br mixing ratio of 5.8 ppt. These results extend the existing historical record derived from air and Antarctic firn air to about 350 years before present. Model simulations illustrate that the ice core results are consistent with estimates of the impact of anthropogenic activity (fumigation, combustion, and biomass burning) on the atmospheric CH3Br burden, given the large current uncertainties in the modern atmospheric CH3Br budget. A preindustrial scenario assuming no fumigation, no combustion, and a 75% reduction in biomass-burning sources yields a Southern Hemisphere mean mixing ratio of 5.8 ppt, in good agreement with the ice core results. There is a significant imbalance between the known CH3Br sources and sinks in the modern atmospheric CH3Br budget. The ice core data do not sufficiently constrain the model to determine how much of the “unknown source” was present in the preindustrial budget. The results do indicate that most of the southern hemispheric component of this “unknown source” is not anthropogenic.” [Full text]

A history of chemically and radiatively important gases in air deduced from ALE/GAGE/AGAGE – Prinn et al. (2000)“We describe in detail the instrumentation and calibrations used in the Atmospheric Lifetime Experiment (ALE), the Global Atmospheric Gases Experiment (GAGE), and the Advanced Global Atmospheric Gases Experiment (AGAGE) and present a history of the majority of the anthropogenic ozone-depleting and climate-forcing gases in air based on these experiments. … Some specific conclusions are as follows: (1) International compliance with the Montreal Protocol is so far resulting in chlorofluorocarbon and chlorocarbon mole fractions comparable to target levels; (2) mole fractions of total chlorine contained in long-lived halocarbons (CCl2F2, CCl3F, CH3CCl3, CCl4, CHClF2, CCl2FCClF2, CH3Cl, CH2Cl2, CHCl3, CCl2=CCl2) in the lower troposphere reached maximum values of about 3.6 ppb in 1993 and are beginning to slowly decrease in the global lower atmosphere; (3) the chlorofluorocarbons have atmospheric lifetimes consistent with destruction in the stratosphere being their principal removal mechanism; (4) multiannual variations in chlorofluorocarbon and chlorocarbon emissions deduced from ALE/GAGE/AGAGE data are consistent approximately with variations estimated independently from industrial production and sales data where available (CCl2F2 (CFC-12) and CCl2FCClF2 (CFC-113) show the greatest discrepancies);” [Full text]

A record of atmospheric halocarbons during the twentieth century from polar firn air – Butler et al. (1999)“Measurements of trace gases in air trapped in polar firn (unconsolidated snow) demonstrate that natural sources of chlorofluorocarbons, halons, persistent chlorocarbon solvents and sulphur hexafluoride to the atmosphere are minimal or non-existent. Atmospheric concentrations of these gases, reconstructed back to the late nineteenth century, are consistent with atmospheric histories derived from anthropogenic emission rates and known atmospheric lifetimes. The measurements confirm the predominance of human activity in the atmospheric budget of organic chlorine, and allow the estimation of atmospheric histories of halogenated gases of combined anthropogenic and natural origin. The pre-twentieth-century burden of methyl chloride was close to that at present, while the burden of methyl bromide was probably over half of today’s value.” [Full text]

Growth of fluoroform (CHF3, HFC‐23) in the background atmosphere – Oram et al. (1998)“We have found that present‐day HFC‐23 concentrations (c. 11 pptv in late 1995) exceed those of SF6 by a factor of three. Concentrations have steadily increased in the atmosphere since at least 1978, and are continuing to do so at a present rate of 5% per year. Furthermore, HFC‐23 appears to be long‐lived in the atmosphere, with a stratospheric lifetime of at least 1000 years, and a modelled tropospheric lifetime of 230 years.”